Flow control valves are used extensively to control fluid flow in heating and cooling systems used to control thermal loads in, as an example, buildings or other spaces. Conventional heating and chilled water systems system utilized the flow control valves control the flow of fluid through the system as needed to meet the heating or cooling needs, such as may be indicated by a thermostat or other control system. The systems also typically monitor the amount of energy being used in the heating and chilled water system via BTU (British Thermal Units) meters.
BTU meters are used in buildings to measure heat consumed in building HVAC systems for both performance monitoring and billing purposes. BTU meters for building applications are most commonly comprised of a computer connected to a liquid flow meter and temperature sensors before and after a heating or cooling load. The flow rate measured multiplied by the temperature difference across the heating or cooling coil multiplied by a constant is equal to the BTUs transferred to (cooling) or from (heating) the load.
U.S. Pat. No. 5,904,292 discloses an electrically driven valve connected to a cooling or heating load, such as a coil, with temperature sensors before and after the coil with the system controlled and monitored by a computer. This valve is not a pressure balanced device so a change in pressure drop across the valve section would result in change in flow rate measured in the built in flow meter. The motor would then need to adjust the stem. While making this adjustment valves in parallel with the valve undergoing adjustment would then be effected with respect to pressure drop. The result of the interdependence on all valves is that the flow rates will cycle in rate never reaching a constant flow through the heating or cooling coil.